From 93ad0edf674125f19177054d8331a5e8910d3d98 Mon Sep 17 00:00:00 2001
From: Fangrui Song <i@maskray.me>
Date: Tue, 12 Jan 2021 00:07:28 -0800
Subject: [PATCH] [ELF] Drop .rel[a].debug_gnu_pub{names,types} for --gdb-index
 --emit-relocs

Fixes PR48693: --emit-relocs keeps relocation sections. --gdb-index drops
.debug_gnu_pubnames and .debug_gnu_pubtypes but not their relocation sections.
This can cause a null pointer dereference in `getOutputSectionName`.

Also delete debug-gnu-pubnames.s which is covered by gdb-index.s

Reviewed By: grimar

Differential Revision: https://reviews.llvm.org/D94354
---
 lld/ELF/SyntheticSections.cpp     |  7 +++++++
 lld/test/ELF/debug-gnu-pubnames.s | 18 ------------------
 lld/test/ELF/gdb-index.s          | 15 ++++++++++-----
 3 files changed, 17 insertions(+), 23 deletions(-)
 delete mode 100644 lld/test/ELF/debug-gnu-pubnames.s

diff --git a/lld/ELF/SyntheticSections.cpp b/lld/ELF/SyntheticSections.cpp
index 9b5fb3f26c59..9a875bd7ec3e 100644
--- a/lld/ELF/SyntheticSections.cpp
+++ b/lld/ELF/SyntheticSections.cpp
@@ -2879,6 +2879,13 @@ template <class ELFT> GdbIndexSection *GdbIndexSection::create() {
     else if (isec->name == ".debug_info")
       files.insert(isec->file);
   }
+  // Drop .rel[a].debug_gnu_pub{names,types} for --emit-relocs.
+  llvm::erase_if(inputSections, [](InputSectionBase *s) {
+    if (auto *isec = dyn_cast<InputSection>(s))
+      if (InputSectionBase *rel = isec->getRelocatedSection())
+        return !rel->isLive();
+    return !s->isLive();
+  });
 
   std::vector<GdbChunk> chunks(files.size());
   std::vector<std::vector<NameAttrEntry>> nameAttrs(files.size());
diff --git a/lld/test/ELF/debug-gnu-pubnames.s b/lld/test/ELF/debug-gnu-pubnames.s
deleted file mode 100644
index 51a289e52558..000000000000
--- a/lld/test/ELF/debug-gnu-pubnames.s
+++ /dev/null
@@ -1,18 +0,0 @@
-# REQUIRES: x86
-# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
-
-# RUN: ld.lld %t.o -o %t1.exe
-# RUN: llvm-readobj --sections %t1.exe | FileCheck %s
-# CHECK: .debug_gnu_pubnames
-# CHECK: .debug_gnu_pubtypes
-
-# RUN: ld.lld --gdb-index %t.o -o %t2.exe
-# RUN: llvm-readobj --sections %t2.exe | FileCheck %s --check-prefix=GDB
-# GDB-NOT: .debug_gnu_pubnames
-# GDB-NOT: .debug_gnu_pubtypes
-
-.section .debug_gnu_pubnames,"",@progbits
-.long 0
-
-.section .debug_gnu_pubtypes,"",@progbits
-.long 0
diff --git a/lld/test/ELF/gdb-index.s b/lld/test/ELF/gdb-index.s
index 546590ab359e..54a01a2c0d51 100644
--- a/lld/test/ELF/gdb-index.s
+++ b/lld/test/ELF/gdb-index.s
@@ -5,7 +5,14 @@
 
 # RUN: llvm-objdump -d %t | FileCheck %s --check-prefix=DISASM
 # RUN: llvm-dwarfdump -gdb-index %t | FileCheck %s --check-prefix=DWARF
-# RUN: llvm-readelf -sections %t | FileCheck %s --check-prefix=SECTION
+
+## Drop .debug_gnu_pubnames and .debug_gnu_pubtypes.
+## Also drop their relocation sections if --emit-relocs is specified.
+# RUN: ld.lld --gdb-index --emit-relocs %t1.o %t2.o -o %t1
+# RUN: llvm-readelf --sections %t1 | FileCheck %s --check-prefix=SECTION
+
+# SECTION-NOT: .debug_gnu_pubnames
+# SECTION-NOT: .debug_gnu_pubtypes
 
 # RUN: llvm-mc -compress-debug-sections=zlib-gnu -filetype=obj -triple=x86_64-pc-linux \
 # RUN:   %p/Inputs/gdb-index.s -o %t2.o
@@ -46,8 +53,6 @@
 # DWARF-NEXT:    1(0x8): 0x30000000
 # DWARF-NEXT:    2(0x10): 0x90000000 0x90000001
 
-# SECTION-NOT: debug_gnu_pubnames
-
 # RUN: ld.lld --gdb-index --no-gdb-index %t1.o %t2.o -o %t2
 # RUN: llvm-readobj --sections %t2 | FileCheck -check-prefix=NOGDB %s
 # NOGDB-NOT: Name: .gdb_index
@@ -111,7 +116,7 @@ entrypoint:
 .section .debug_gnu_pubnames,"",@progbits
 .long 0x1e
 .value 0x2
-.long 0
+.long .debug_info
 .long 0x33
 .long 0x18
 .byte 0x30
@@ -121,7 +126,7 @@ entrypoint:
 .section .debug_gnu_pubtypes,"",@progbits
 .long 0x17
 .value 0x2
-.long 0
+.long .debug_info
 .long 0x33
 .long 0x2b
 .byte 0x90